Method of indicating electric currents



(No Model.)

0'. B. SHALLENBERGER.

METHOD OF INDIOATING ELECTRIC GURRENTS. No. 383,672. Patented May 2 9, 1888.

WITNESSES:

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Nrrn STATES OLIVER B. SHALLEN BERGER, OF ROCHESTER, ASSIGNOR TO THE VVESTING- HOUSE ELECTRIC COMPANY, OF PITTSBURG, PENNSYLVANIA.

. METHOD OF INDICATlNG ELECTRIC CURRENTS SPECIFICATION forming part of Letters Patent No. 383,672, dated May 29, 1888. Application filed January 21, 1888. Serial No. 261,4'l1. (No model.)

To all whom it may concern:

Be it known that I, OLIVER B. SIIALLEN- BERGER, a citizen of the United States, residing in Rochester, in the county of Beaver, in

the State of Pennsylvania, have invented certain new and useful Improvements in the Method of Indicating ElectricGurrents, (Case 199,) of which the following is a specification.

The invention relates to the class of appa- [O ratus employed for indicating the strength of current upon an electric circuit.

The object of the invention is to provide a convenient, effective, and reliable method for determining the difference of potential existing between two given points in an electric circuit supplied with alternating, intermittent, or pulsatory electric currents.

It is well known that the value of a given electric current is proportional to the electromotive force to which it is due, divided by the resistance which it encounters. If, therefore, the resistance is decreased at the same time that the electro-motive force is increased, or vice versa, then the current flowing will increase or decrease at a rate greater than the increase or decrease of the eleetromotive force. The present invention aims to substitute for such variable resistances a variable counter electro-motive force, the amount of which is 0 dependent upon the variations in the difference of potential to be determined. A circuit having an appreciable self-induction when traversed by alternating, intermittent, or pulsatory electric currents opposes a counter elec- 5 tromotive force varying in the manner required for this purpose that is to say, as the current traversing it increases the apparent resistance due to selfinduction diminishes, and vice versa, although the actual specific resistance remains constant. 1t is possible to give to inductive devices of different forms or proportions different rates of increase or decrease of current under the influence of the same variations of the difference of potential,

5 and therefore a current traversing two such inductive resistances in series or parallel will produce a combined effect different from that in either acting separately.

In general terms, the invention may be de scribed as follows: An electric conductor having a high self-induction is connected between the points at which it is desired to determine the difference of potential, and also an adjustable resistance and a solenoid or electromagnet or other suitable means for operating the indicating device. N ow,as the current through these devices increases the counter electro-motive force developed by reason of the self-induction also increases, but in graduallydecreasing ratio. This variation is proportional to the variation in the electro-motive force,and for this reason the variation of current through the circuit is greater than the variation of electro-motive force. Thus it will be understood that slightvariations in difference of potential will be much more readily indicated.

Variable resistances in the form of incandescent electric lamps have been employed for similar purposes; but certain objections are found in their use. For instance, they are fragile, they do not permit of such ready adjustment as the self-inductors, and even after careful adj ustment are liable to change greatly in resistance, and so render the indications of the instrument valneless. By the use of this invention fixed or adjustable resistances may be employed throughout, so that the liability to change is reduced to a minimum, while at the same time even greater seusitiveness may be obtained than by theemployment of a varying resistance.

In an application of even date herewith, Serial No. 261,467, the apparatus here shown is claimed.

In the accompanying drawings, Figure 1 is a diagram illustrating an organization of ap paratus for carrying out th'einvention. Figs. 2 and 3 illustrate modifications.

Referring to Fig. 1, A represents a suitable source of alternating, intermittent, or pulsatory electric currents; L L", the main lines leading to any suitable work-circuit. Between the lines L and L there is connected the indicating apparatus to be described. This con sists, in this instance, of an indlieator, D. (Here shown as consisting of a lever, d, carrying a pointer, 6, applied to ascale-plate, f.) From one end of the beam 12 there is sus pended a core, g, extending into a solenoid, h. A counterpoise, i, is suspended from the opposite end of the beam (1. The solenoid h is included in a conductor, Z, extending from coil h.

the line L to theline L, beiugconnected therewith at the points 1 and 2. A coil, M, of high Self-induction, is included in series with the This coil M is provided with a core, in, of soft iron. This core, as also the core g, is preferably made up of fine soft iron wires, or laminae of soft iron. An adjustable resistance, M, is also included in series with the coils M and h.

The method of determining the electrometive force is simply to establish a given normal current through the coil M of high'selfinduction by placing a fixed difference of potential upon'it, and noting the amount of resistance which mustbe introduced into the circuit in order to establish this normal difference of potential-that is to say, the instrument will only balance, bringing the pointer e at the center of the plate f, when a certain predetermined difference of potential is maintained between the points 3 and 4 upon the opposite sides of the coil M and solenoid h, the additional difference of potential at the terminals of the resistance M being determined by the position of the indicator it upon the scale a.

The resistance M may be included in shunt upon the self-inductor M, as shown in dotted lines, in some instances.

The effect of the self-induction device is to render the instrument much more sensitive than would be the case if a fixed resistance were employed, for, as has been pointed out, its apparent resistance decreases as the electro-motive force increases. If the rate of alternations of orperiodic changes in the current should remain approximately the same, no adjustment of the resistance M is necessary in order to insure the accurate operation of this instrument. This condition is fulfilled in those systems of electric distribution where all the machines are intended to run at approximately the same number of alternations per minute, say sixteen thousand 5 but where there are slight variations in the number of alternations of the current, the self-induction will vary with the rate of alternation as well as with the electro-motive force, but the adjustable resistance device M may be used as a correction for the slight variations thus occasioned. The error due to this cause is usually very small; but in some instances this adj ustment may be desirable.

In Fig. 2 a modification is shown'wherein the amount of self-induction in the circuit can be varied; This can be accomplished by moving the core m of the self-induction device M within its coil. The resistance M and device D areincluded in the circuit, as before. In

this instance a converter, 0, is interposed between the lines 1'2 and Z Z the former being connected from the line L to the line L through the primary coil 19 of the converter. The conductor 1 is connected through the secondary coils and the devices M, M, and D. The converter serves to reduce the current in any required proportion, so as to makeit more convenient for handling.

The adjustment of the device M serves also to correct for the variations in the rate of alternations, if it is so desired. I

In Fig. 3 there is shown an organization by means of which slight changes in the rate of alternation may be compensated for automatically. Two self-induction devices, M and M of different forms,are employed, and they may be so proportioned that while an increase in the number of alternations mayincrease the self-induction of one it will have the opposite effect upon the other. Itisa well-known property of coils possessing a self-induction, 1n which an iron core is present, that there is a particular point at which the self-induction remains approximately constant through a considerable changein the rate of alternations, while it decreasesboth above and below this point. It is therefore necessary to suitably proportion the two coils and use one above its particular approximately constant point, and the other below such point, in order to compensate within certain limits for the error due to changes in the rate of alternation. The coil of the indicating apparatus h may be utilized in certain cases for this purpose by male ing it of suitable form and proportion, thus dispensing with the use of aseparate compensating coil.

The two coils M and M might be connected in parallel with each other in the same manner as the coil M and the resistance M in Fig. 1.

Any convenient form of indicating device may be employed in place of the one shown as, for instance, a Siemens clectro-dynamometer.

I claim as my invention- 1. The hereinbefore-described method of measuring the difference of potential existing between two points in an electric circuit for alternating, intermittent, or pulsatory electric currents, which consists in determining the amount of resistance required in a circuit of high self-induction through whichsaid points are connected to establish a definite current therein. r

2. The hereinbefore-described method of determining the variations in the difference of potential between two points in an electric circuit foralternating, intermittent, or pulsatory electric currents, which consists in establishing in the circuit connecting said points intermittent, or pulsatory electric currents,

which consists in establishing a definite current through a circuit of high self-induction, connecting the points by varying an adjustable resistance connected in the circuit,and noting tial at the terminals of an adjustable resistance the amount of such variations. connected in the same circuit.

4. The hereinbefore-described method of in- In testimony whereof I have hereunto subdicating the difference of potential between scribed my name this 10th day of January, 5 two points in an electric circuitfor alternating, A. D. 1888.

intermittent, or pulsatory electric currents,

which consists in establishing a difference of OLIVER SHALLENBERGER' potential at the terminals of a coil of high Witnesses: self-induction which derives currentfrom that W. D. UPTEGRAFF,

" IO circuit and in adding the difference of poten- DANL. W. EDGEOOMB. 

